Synthesis of photoreactive polymeric binders

ABSTRACT

A photoreactive binder that may be used to enhance photospeed in either conventional plates or on-press developable lithographic printing plates. Briefly, a polymer of m-isopropenyl-α,α-dimethylbenzyl isocyanate is derivatized for vinyl group reactivity by reacting the isocyanate groups thereof with hydroxyalkyl acrylate. The resulting photopolymeric binder provides significantly higher photospeed than the non-reactive binder currently utilized in the production of conventional printing plates. The resulting lithographic printing plate also shows better durability (as manifested by longer run-length) and is more easily developed by the microencapsulated developers utilized in the present invention. As to the preparation of the photoreactive binders, the application discloses a method of copolymerizing m-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) through complexation with an electron-deficient monomer such as maleic anhydride to accelerate free radical copolymerization with other monomers, and thus, provides greater monomer-to-polymer conversion. Use of the resulting product in the photoresist of a lithographic printing plate improves its adhesion to an underlying substrate.

This application is a division of application Ser. No. 08/429,804, filedApr. 27, 1995, now U.S. Pat. No. 5,514,522, which is acontinuation-in-part of application Ser. No. 08/146,711, filed Nov. 1,1993, abandoned.

FIELD OF THE INVENTION

In general, the several composition and method manifestations of thepresent invention relate to photoreactive polymeric binders, and moreparticularly, to photoreactive polymeric binders capable of beingreadily and functionally incorporated into planographic photoresists toimprove durability while concurrently maintaining and/or enhancingphotosensitivity.

CROSS-REFERENCE TO RELATED APPLICATIONS

U.S. patent application Ser No. 08/146,710, filed on Nov. 1, 1993 nowU.S. Pat. No. 5,516,620 by L. C. Wan, A. C. Giudice, J. M. Hardin, C. M.Cheng, and R. C. Liang, commonly assigned, and titled "On-PressDevelopable Lithographic Printing Plates", describes a lithographicprinting plate for use on a printing press, with minimal or noadditional processing after exposure to actinic radiation. The platecomprises a printing plate substrate, a polymeric resist layer capableof imagewise photodegradation or photohardening, and a plurality ofmicroencapsulated developers capable of blanket-wise promoting thewashing out of either exposed or unexposed areas of the polymericresist. The microencapsulated developers may be integrated into thepolymeric resist layer, or may form a separate layer deposited atop thepolymeric resist layer, or may be coated onto a separate substratecapable of being brought into face-to-face contact with the resistlayer.

U.S. patent application Ser. No. 08/147,044, filed Nov. 1, 1993 nowabandoned by F. R. Kearney, J. M. Hardin, M. J. Fitzgerald, and R. C.Liang, commonly assigned, and titled "Lithographic Printing Plates withPlasticized Photoresists", discloses the use of plasticizers,surfactants and lithium salts as development aids for negative-working,on-press developable lithographic printing plates. Briefly,plasticizers, which are dispersible or soluble in press fountainsolutions and soluble in acrylic monomers and oligomers, areincorporated into a photoresist. Such plasticizers make the photoresistmore permeable to fountain solution prior to crosslinking, while beingeasily extracted with ink and fountain solution after crosslinking. Thesurfactants facilitate the dispersion of hydrophobic imagingcompositions in the fountain solution and reduce scumming. Further,lithium salts may also be incorporated into the photoresist to disrupthydrogen bonding of, for example, urethane acrylate polymers which tendto associate by hydrogen bonding, thus enhancing developability.

U.S. patent Ser. No. 08/146,479, filed Nov. 1, 1993 now abandoned by L.C. Wan, A. C. Giudice, W. C. Schwarzel, C. M. Cheng, and R. C. Liang,commonly assigned, and titled "Lithographic Printing Plates andDispersed Rubber Additives", describes the use of rubbers andsurfactants to enhance the durability of on-press developable printingplates. The rubbers are preferably incorporated into a photoresist asdiscrete rubber particles. To ensure a uniform and stable dispersion,the rubber components are suspended in the photoresist preferably bymeans of surfactants having HLBs approximately between 7.0 and 18.0.

The disclosures of the aforementioned copending applications are herebyincorporated by reference.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

At the present time, virtually all printed copy is produced through theuse of three basic types of printing plates. One type is a relief platewhich prints from a raised surface. Another type is an intaglio platewhich prints from a depressed surface. The third type is thelithographic plate which prints from a substantially flat surface whichis neither appreciably raised above nor appreciably depressed below theadjacent and surrounding non-printing areas. Printing is occasioned byan ink's respective affinity and/or aversion to areas of differentchemical properties. Lithographic printing plates are commonly processedto have water-repellent (hydrophobic), oil-receptive (oleophilic) imageareas and water-receptive (hydrophilic) non-image areas.

Prior to processing for use, conventional lithographic plates willtypically have a hydrophobic, photoreactive polymeric layer (i.e.photoresist) coated or otherwise deposited atop a hydrophilic substrate.

In preparing a conventional lithographic plate for use on a printingpress, the plate is first exposed to actinic radiation. Specificchemical reactions are caused to occur in the plate's photoresist byexposure to actinic radiation. Such photoinduced chemical reactions mayeither reduce or enhance the solubility of the photoresist, depending onwhether the resist is negative-working or positive-working. Innegative-working plates, exposure to actinic radiation will generallycause a "hardening" of the photoresist. In positive-working plates,exposure to actinic radiation will generally cause a "softening" or"solubilization" of the photoresist.

After photoexposure, a wet development step is normally conducted. Theobjective of such wet development is to provide preferential solvationof the areas of the photoresist which have undergone photoinducedchemical change. Solvation under conventional development techniqueswill typically involve treating the exposed plate with organic solventsin a developing bath. For negative-working resists, the solvent willswell and dissolve the unexposed portions of the resist. The solventshould not swell the exposed portions or distortion of the developedimage may result. For positive-working resists, the response of theunexposed and exposed coatings are reversed, but the same generalprinciples apply.

As a result of the preferential solvation and washing away of portionsof the photoresist, corresponding portions of the underlying hydrophilicsubstrate are uncovered. For negative-working plates, the aforementionedhydrophobic image areas correspond to the portions of the photoresistremaining after solvation and washing. The aforementioned hydrophilicnon-image areas correspond to uncovered portions of the substrate. Theimage and non-image areas thus differentiated, the processed plate maythen be mounted onto a printing press and run.

Encumbered by required wet development, the processing of conventionallithographic plates prior to their use on a printing press is time andlabor consuming and involves the use of substantial quantities oforganic chemicals. It will be appreciated that there is considerableattractiveness for innovations that would satisfactorily eliminate orreduce conventional lithography's long-felt dependency upon the conductof wet development and thereby permit the use of lithographic plates ona printing press immediately after exposure without requiredintermediary processing.

In the past, dry-developable lithographic printing plates have beensuggested which enable the wet processing steps of lithographic printingplates after exposure to be omitted and printing to be conducted bydirectly mounting the exposed plates on a printing press. Among printingplates that may be characterized as "on-press" developable (or relatedthereto) are: e.g., U.S. Pat. No. 4,273,851, issued to Muzyczko et al.on Jun. 16, 1981; U.S. Pat. No. 4,879,201, issued to Hasegawa on Nov. 7,1989; U.S. Pat. No. 4,916,041, issued to Hasegawa et al. on Apr. 10,1990; U.S. Pat. No. 4,999,273, issued to Hasegawa on Mar. 12, 1991; andU.S. Pat. No. 5,258,263, issued to Z. K. Cheema, A. C. Giudice, E. LLanglais, and C. F. St. Jacques on Nov. 2, 1993.

Despite the methodologies and approaches embodied in the aforementionedpatents, there is a continuing need for a lithographic printing platethat can be readily developed on a printing press and that produces aplate having durable image areas needed for good run length. Difficultyin the realization simultaneously of both "on press developability" and"durability" is believed to originate from an apparent contradictionbetween photoresist removability ("developability") on the one hand and"durability" on the other: To make a photoresist more durable was tomake the photoresist less developable.

The present invention seeks to more closely align the competing goals of"durability" and "developability" by utilizing photoreactive, polymericbinders capable of effectively functioning as both a matrix and as aphotoreactive component.

In conventional lithographic printing plates, polymeric binders areincorporated into the photoresist to provide film forming propertiesduring coating and to act as the physical backbone or matrix for theresulting photopolymerized structure resulting from exposure. Sinceconventional wet development techniques are oftentimes based upon theuse of strong solvents, tough and comparatively durable polymericbinders may be utilized. The dictates of more narrowly definedparameters for "on press developability", govern latitude in choice ofphotoresist components, in general, and effectively preclude the use oftough and durable binders or other components that may not be removableunder the conditions of a lithographic printing operation.

By way of illustration, in the U.S. patent application Ser. No.08/146,710 cross-referenced above and entitled "On-Press DevelopableLithographic Printing Plates", on-press development is effectuated bythe use of high-boiling point, low-vapor pressure developers. Thesecomparatively weak developers solubilize portions of the photoresistsuch that they may be easily washed away "on-press" by fountain and inksolutions. In this, and like systems, binders that are less durable butmore easily dispersed in fountain and ink solutions are favored.However, with such binders, durability is compromised.

In order to compensate for the losses in durability, a photoresist maybe designed thicker and with a larger proportion of binder to preventtackiness. An increase in binder, however, would normally be balanced bya proportionate decrease in photopolymerizable monomers; a concomitantloss of photosensitivity would be expected. It has been found that aprinting plate that can be developed effectively "on-press" and whichprovides image areas of good durability can be realized by utilizing ina photoresist layer thereof a polymeric binder having both structuraland photoreactive capabilities. While developed in the context of"on-press" developable printing plates, several diverse applications ofthe inventive photoreactive polymeric binder are envisioned and enabledby the present disclosure.

SUMMARY OF THE INVENTION

The present invention provides a photoreactive polymeric binder that maybe used to improve durability while maintaining and/or enhancing thephotosensitivity of a lithographic printing plate. Briefly, in oneembodiment, a photoreactive binder is provided comprising a derivatizedcopolymer of m-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) and anethylenically unsaturated comonomer. In a method aspect, m-TMI iscopolymerized with an ethylenically unsaturated monomer and subsequentlyderivatized for vinyl group reactivity by reacting the isocyanate groupsthereof with a hydroxyalkyl acrylate. The resulting photopolymericbinder provides significantly higher photospeed than the non-reactivebinder currently utilized in the production of conventional printingplates. The resulting lithographic printing plate also shows betterdurability (as manifested by longer run-length) and is more easilydeveloped by high-boiling point, low-vapor pressure developers. As tothe preferred preparation of preferred photoreactive binders, theapplication describes a method of copolymerizingm-isopropenyl-α,α-dimethylbenzyl isocyanate (m-TMI) through complexationwith an electron-deficient monomer such as maleic anhydride toaccelerate free-radical copolymerization with other monomers, thusproviding greater monomer to polymer conversion, and higher molecularweight particularly for polymers containing a high degree of m-TMIsubstitution. Use of the resulting product in the photoresist of alithographic printing plate improves its adhesion to an underlyingsubstrate, and thus enhances durability.

In this light, it is an objective of the present invention to provide aphotoreactive polymeric binder which may be incorporated into aphotopolymerizable, photocrosslinkable or otherwise photorearrangeablecomposition to effectuate both higher photosensitivity and greaterdurability.

It is another object of the present invention to provide a high speed,non-tacky lithographic printing plate that may be utilized effectivelywith a microencapsulated developer system.

It is another object of the present invention to provide an efficientand effective process for producing durable and photosensitivephotoresists.

It is another objective of the present invention to provide aphotoreactive polymeric binder comprising a derivatized copolymer ofm-isopropenyl-α,α-dimethylbenzyl isocyanate and an ethylenicallyunsaturated comonomer.

It is another objective of the present invention to provide a method ofsynthesizing a photoreactive polymeric binder by copolymerizingm-isopropenyl-α,α-dimethylbenzyl isocyanate with an ethylenicallyunsaturated comonomer, and derivatizing the isocyanate groups thereofwith a hydroxyalkyl acrylate or hydroxyalkyl methacrylate.

It is another objective of the present invention to provide aphotoreactive polymeric binder comprised of a derivatized copolymer ofm-isopropenyl-α,α-dimethylbenzyl isocyanate, ethylenically unsaturatedcomonomers, and maleic anhydride.

It is another object of the present invention to provide a method ofsynthesizing a photoreactive polymeric binder by utilizing maleicanhydride as a "matchmaker" to give higher monomer-to-polymerconversion, higher molecular weight binder and potential pendantcarboxylic acids for improved adhesion and/or developability.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this disclosure the term "on-press" is used to describe bothdevelopment and printing plates, (e.g., "on-press development","developing on-press" and "on-press developable lithographic printingplates"). As used herein, the modifier "on-press" will be defined asindicating an ability to develop a useful imagewise distribution ofoleophilic and hydrophobic polymeric areas on a printing press afterimagewise exposure, without resort to wet development steps or likeintermediary processing. "On-press" techniques should be contrasted withother so-called "dry development" techniques: e.g., dry collotype andlaser ablation techniques, wherein oleophilic and hydrophobic imageareas are formed at exposure; and peel-apart and thermal transfertechniques, wherein oleophilic and hydrophilic image areas are formedafter a laminar separation.

In embodiments most closely related to the field of lithography, thepresent invention provides a photoresist system which is comprised of atleast a photosensitive polymerizable monomer and a photoreactivepolymeric binder. As formulated, the photoresist system may be preparedas a coating which may be deposited on a suitable lithographic printingplate substrate. Upon photoexposure, exposed regions of the printingplate's photoresist coating are hardened by the effects ofhomopolymerization of the polymerizable monomer and by graftpolymerization or cross linking involving the photoreactive polymericbinder. The resulting printing plate may be developed throughconventional methods or through the innovative processes describedbriefly below and more fully in the cross-referenced applications.

According to one embodiment of the invention, a photoreactive bindercomprises a copolymer of repeating units of a derivatizedm-isopropenyl-α,α-dimethyl isocyanate (m-TMI) and repeating units froman ethylenically unsaturated copolymerizable monomer, the polymer havingthe having the following chemical structure, CS(I): ##STR1## wherein--M-- represents polymerized units of ethylenically unsaturatedmonomers; n is an integer from 1 to 18, preferably from 2 to 6; byweight, y is approximately 70 to 95%, preferably 80 to 90%, and, z isfrom approximately 5 to 30%, preferably greater than 10%; R₁ is H, or analkyl group, such as a methyl group.

Ethylenically unsaturated monomers that may be used with the presentinvention may be selected by one skilled in the art in view of thepresent disclosure. Typically, the ethylenically unsaturated monomerswill have the formula H₂ C═CR₄ R₅, wherein R₄ and R₅ are each H, Cl, analkyl group, such as a methyl group, --CO₂ CH₃, --CO₂ CH₂ CH₃, --CO₂ Bu,--CO₂ C₈ H₁₇, --CO₂ C₁₂ H₂₅, --CO₂ Ph, --CO₂ CH₂ CH₂ N(CH₃)₂, --Ph,--CN, --C₆ H₄ CH₂ Cl, --C₆ H₄ N, --F, --COOH, --SO₃ H, or their salts.Ethylenically unsaturated monomers substituted for added functionalityare also contemplated.

The photoreactive copolymer of chemical structure (I) is obtained bycopolymerizing an m-isopropenyl-α,α-dimethyl isocyanate monomer withcopolymerizable ethylenically unsaturated monomers (M', below) andderivatizing the pendant isocyanates of the intermediate copolymer witha hydroxyalkyl acrylate or methacrylate, such as 4-hydroxybutylacrylate. This process is illustrated by the following Synthesis Scheme,SS (I): ##STR2##

Radical copolymerization, step 1 in Synthesis Scheme (I), is performed,for example, in either the presence of a thermal initiator such as2,2'-azobis-(2-methylpropionitrile), AIBN, in methyl ethyl ketone, MEK,at 70° C., or t-butyl peroxybenzoate, t-BPB, in refluxing toluene.Reference may be made to the examples, infra, for representativeillustration. Other suitable polymerization initiators are known in theart and can be used in the practice of the present invention.

Derivatization, step 2 in Synthesis Scheme (I), is done in the presenceinitially of radical inhibitors such as 2,6-di-t-butyl-4-methylphenol(BHT) and air, then catalysts for the urethane reaction such as dibutyltin dilaurate (DBTDL), triethylamine, and esters ofp-dimethylaminobenzoic acid. Reference may be made to the examples,infra, for representative illustration.

It is noted that while 4-hydroxybutyl acrylate (HBA) is the preferredcompound for derivatization, other hydroxyalkyl acrylates andmethacrylates as well as other vinyl substituted compounds may be used.Examples of such compounds are 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxpropyl acrylate, 4-hydroxybutyl vinyl ether, allylalcohol.

The subject of matter represented by Synthesis Scheme (I) and chemicalstructure (I) are encompassed in U.S. patent application Ser. No.08/147,045.

According to a second and preferred embodiment of the invention, maleicanhydride is utilized (as a "matchmaker") to increase the"monomer-to-polymer" conversion rate of a radical copolymerization stepset forth in, for example, step 1 of Synthesis Scheme (I). In thisregard, it will be appreciated that maleic anhydride has an electronpoor double bond that may form a charge transfer complex withelectron-donor monomers such as styrene, α-methylstyrene, vinyl ethersand vinylcarbazole, forming alternate copolymers. The donor-acceptormonomers can then copolymerize with a third "neutral" monomer such asmethyl methacrylate or 2-chloroethyl methacrylate. With regard to itsuse in accelerating m-TMI copolymerization, maleic anhydride(functioning as an acceptor) may complex with m-TMI (functioning as adonor), and thereby accelerate free-radical copolymerizations with otherethylenically unsaturated comonomers. Maleic anhydride molecules whichare not complexed with m-TMI, may still react favorably with m-TMIradicals and result in maleic anhydride radicals which in turn reactfavorably with acrylate or methacrylate monomers. Electron deficientmonomers such as maleic anhydride significantly accelerate the rate andconversion, as well as increase molecular weight as compared to thecopolymerization of m-TMI and the ethylenically unsaturated comonomersalone, particularly when the concentration of m-TMI is high in themonomer composition. Aside from maleic anhydride, other useful electrondeficient monomers include maleate esters (e.g., diethyl maleate,dibutyl maleate), fumarate esters, and fumaronitrile. In certainequivalent embodiments, maleic anhydride may be replaced (completely orin part) with, for example, n-butyl maleimide. Regardless, maleicanhydride is preferred.

In contrast to the polymeric binders of the first embodiment, i.e.chemical structure (I), the photoreactive polymeric binder synthesizedthrough the maleic anhydride accelerated copolymerization are comprisedof polymers having the following generic chemical structure, CS (II):##STR3## wherein --M--, R₁, n, y and z in chemical structure (II) are asdescribed for chemical structure (I); the sum of v and x are fromgreater than 0 to approximately 10%, and R₂ and R₃ are H, alkyl or arylgroup, and more preferably --(CH₂)_(n) O₂ CCH═CH₂. In a presentlypreferred embodiment, the sum of v and x is approximately 5% by weight;z is approximately 12% by weight; and y is approximately 86% by weight.

The photoreactive polymeric binders of chemical structure (II) areobtained by initially copolymerizing m-TMI with maleic anhydride andother ethylenically unsaturated monomers, such as methyl methacrylateand butyl methacrylate. The introduction of maleic anhydride results inhigher conversion of higher molecular weight compounds. The compoundsare then derivatized with a hydroxyalkyl acrylate, such as4-hydroxybutyl acrylate. The process is illustrated by the synthesisscheme, SS (II): ##STR4##

As with Synthesis Scheme (I), the radical copolymerization step, step 1of Synthesis Scheme (II), can be performed, for example, in the presenceof AIBN in either MEK at 70° C. or t-BPB in refluxing toluene. Referencemay be made to the examples, infra, for representative illustration.Other suitable polymerization initiators are known in the art and can beused in the practice of the present invention.

The protocol for the derivatization step, step 2 of Synthesis Scheme(II), is the same as the derivatization step for Synthesis Scheme (I).It is noted however that upon derivatization, some of the maleicanhydride units are typically hydrolyzed with provision of carboxylicacid groups pendant from the polymer. These pendant groups promotebetter adhesion to the printing plate substrate. Such enhanced adhesionhelps to prevent the photoresist from being undercut from an underlyingsubstrate by fountain solution and thus contributes to greaterdurability.

It will be appreciated, that in the photoresist system of the presentinvention, photohardening of the photoresist layer is effected byreactions involving both the photoreactive binder and the principalphotoactive component of the photoresist composition, for example, aphotopolymerizable, photocrosslinkable or photorearrangeable compound,typically a photopolymerizable ethylenically unsaturated monomer. Theprincipal photoactive component may include, any variety of compounds,mixtures, or mixtures of reaction compounds or materials capable ofbeing physically altered by photoexposure or of promoting physicalalteration (e.g., hardening) of the properties of the layer in areas ofphotoexposure. Compounds and materials suitable for this purpose includemonomeric and oligomeric photopolymerizable compounds which undergofree-radical or cation-initiated addition polymerization. A large numberof useful compounds is available, generally characterized by a pluralityof terminal ethylenic groups.

Especially preferred for promoting photohardening of polymeric resistlayer is a polymerizable monomer which forms a macromolecular orpolymeric material upon photoexposure, preferably a photopolymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup capable of forming a high polymer by free-radical initiated orcation-initiated chain-propagated addition polymerization. Examples ofsuch unsaturated compounds include acrylates, acrylamides,methacrylates, methacrylamides, allyl compounds, vinyl ethers, vinylesters, N-vinyl compounds, styrene, crotonates and the like.Polymerization can be effected by using a photoinitiator, such as afree-radical generating, addition polymerization-initiating systemactivatable by actinic radiation. Such initiating systems are known andexamples thereof are described below.

Preferred polymerizable monomers are the polyfunctional acrylatemonomers, such as the acrylate and methacrylate esters of ethyleneglycol, trimethylolpropane and pentaerythritol. These can be polymerizedin exposed regions of a polymeric photoresist in the presence of aphotoinitiator. Suitable photoinitiators include the derivatives ofacetophenone (such as 2,2-dimethoxy-2-phenylacetophenone), benzophenone,benzil, ketocoumarin (such as 3-benzoyl-7-methoxy coumarin), xanthone,thioxanthone, benzoin or an alkyl-substituted anthraquinone, diaryliodonium salt, triaryl sulfonium salts, azobisisobutyronitrile andazo-bis-4-cyano-pentoic acid, although others can be employed.

The practical concentration of the monomer or monomers employed is about7.5%-70% by weight based on the total solids of the composition, andpreferably between 15-40%.

The photoresist systems of the present invention can be suitably coatedinto a layer which, upon photoexposure, undergoes hardening as theresult of polymerization of the polymerizable monomer and grafting ofthe monomer onto the photoreactive polymeric binder and cross-linkingreactions involving the photoreactive polymeric binder. If desired,other crosslinking agents, such as bisazides and polythiols, can beincluded to promote crosslinking of polymerizable monomer or the binder.

If desired, preformed polymers having pendant pyridium ylide groups,which groups, upon photoexposure, undergo ring expansion(photorearrangement) to a diazepine group with accompanyinginsolubilization can also be blended with the photoreactive polymer ofthis invention. Examples of polymers having such pyridium ylide groupsare set forth in U.S. Pat. No. 4,670,528, issued to L. D. Taylor and M.K. Haubs on Jun. 2, 1987.

To prepare a lithographic plate according to an embodiment of thepresent invention, the photoresist system is deposited as layer onto asubstrate. Certain factors are considered in determining the appropriatematerials for the substrate. Such factors vary with the particularlithographic needs of individual projects and are believed to be withinthe grasp of one skilled in the pertinent art. Regardless, for mostlithographic needs envisioned, suitable substrates will generallyinclude those to which the polymeric resist layer can be adheredadequately, prior to photoexposure, and to which photoexposed printing(image) areas are adhered after photoexposure. Other pertinentconsiderations may be extrapolated on the basis of the presentdisclosure.

In practice, substrate materials for use in the manufacture of printingplates will oftentimes be subjected to one or more treatments in orderto improve adhesion of the photoresist, or to increase the hydrophilicproperties of the substrate material, and/or to improve thedevelopability of the photoresist, as is described in U.S. Pat. No.4,492,616 (issued Jan. 8, 1985 to E. Pliefke, et al.). Thus, thesubstrates will typically be treated (for example, withpolyvinylphosphonic acid or silicate or by anodization, or by coronadischarge or plasma treatment, or by roughening or graining treatment)to promote desired adhesion of the polymeric photoresist.

Especially preferred substrates are the metallic substrates of aluminum,zinc, steel or copper. These include the known bi-metal and tri-metalplates such as aluminum plates having a copper or chromium layer; copperplates having a chromium layer; steel plates having copper or chromiumlayers; and aluminum alloy plates having a cladding of pure aluminum.Other preferred substrates are silicone rubbers and metallized plasticsheets such as poly(ethylene terephthalate).

Preferred plates are the grained, anodized aluminum plates, where thesurface of the plate is roughened mechanically or chemically (e.g.,electrochemically) or by a combination of roughening treatments.Anodized plates can be used to provide an oxide surface. Still morepreferred plates are anodized aluminum plates which, for example, havebeen treated with polyvinylphosphonic acid or otherwise provided with aresinous or polymeric hydrophilic layer.

Examples of printing plate substrate materials which can be used in theproduction of printing plates of the invention, and methods of grainingand hydrophilizing such substrates are described, for example, in U.S.Pat. No. 4,153,461 (issued May 8, 1979 to G. Berghauser, et al.); theaforementioned U.S. Pat. No. 4,492,616 issued to E. Pliefke, et al.;U.S. Pat. No. 4,618,405 (issued Oct. 21, 1986 to D. Mohr, et al.); U.S.Pat. No. 4,619,742 (issued Oct. 28, 1986 to E. Pliefke); and U.S. Pat.No. 4,661,219 (issued Apr. 28, 1987 to E. Pliefke).

It is common practice in preparing photoresist compositions to employphotosensitizers, coinitiators, and activators. Photosensitizers andcoinitiators are relied upon to capture photons of exposing radiation.They may absorb light of different wavelengths from the principalphotoinitiator. The activator in contrast is not relied upon to responddirectly to exposing radiation, but rather adjacent activator andphotosensitizer molecules react, following excitation of the latter byphoton capture, causing release of a free radical which in turn inducesimmobilization addition reactions at sites of ethylenic unsaturation.

Photoexposure of the printing plates can be accomplished according tothe requirements dictated by the particular composition of the polymericphotoresist and the thickness thereof. In general, actinic irradiationfrom conventional sources can be used for photoexposure, for example,relatively long wavelength ultraviolet irradiation or visibleirradiation. UV sources will be especially preferred and include carbonarc lamps, "D" bulbs, Xenon lamps and high pressure mercury lamps.

The thickness of the photoresist can vary with the particularrequirements. In general, it should be of sufficient thickness toprovide a durable photohardened printing surface. Thickness should becontrolled, however, such that it can be exposed within exposure-timerequirements and should not be applied at a thickness that hampers readyremoval of the layer in non-exposed areas by developers. When utilizingan anodized, grained aluminum substrate, good results are obtained byusing a polymeric photoresist having a thickness in the range of fromabout 0.2 microns to about 3 microns above the microstructure of thegrains, preferably about 0.2 to 0.6 microns "above the grain".

A polymeric photoresist can be provided with colorants, e.g., tint dyes,to provide a desired and predetermined visual appearance. Especiallypreferred will be a colorant, or a precursor of a species, respectively,capable either of being rendered colorless, or being provided withcoloration by the irradiation of the plate-making photoexposure step.Such dye or dye-precursor compounds and the light absorption differencespromoted by the photoexposure allow the platemaker to distinguishreadily the exposed from the non-exposed regions of the plate in advanceof mounting and running the photoexposed plate on a printing press.

In addition, the operability of the polymeric photoresist may beimproved by the addition of other components or additives. For example,the polymeric photoresist can contain plasticizers, hardeners, or otheragents to improve coatability. If desired, macromolecular organicbinders which are non-photoreactive and typically employed in theproduction of photoresist compositions can be employed to advantage. Thepolymeric photoresist may also contain antioxidant materials to preventundesired (premature) polymerization and examples include derivatives ofhydroquinone; methoxy hydroquinone; 2,6-di-(t-butyl)-4-methylphenol;2,2'-methylene-bis-(4-methyl-6-t-butylphenol); tetrakis{methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate} methane;diesters of thiodipropionic acid, triarylphosphite. While the use ofsuch additives is unnecessary for the operability of the presentinvention, incorporation of such additives may dramatically enhanceperformance.

The plasticizers, contrast dyes, imaging dyes and other additives may bemicroencapsulated and incorporated into the photoresist itself or aseparate layer facially positioned or positionable atop the photoresist.Inclusion in the microcapsules would provides a wider latitude in theselection of such additives, since neither the solubility of theadditives in the photopolymerizable compositions nor the inhibition orretardation effect of some additives on polymerization would be an issuein such a system.

For wet development, a diluted alkaline solution optionally containingup to 10% by volume of organic solvents may be used. Examples of usefulalkaline compounds include inorganic compounds such as sodium hydroxide,potassium hydroxide, lithium hydroxide, sodium benzoate, sodium silicateand sodium bicarbonate; and organic compounds such as ammonia,monoethanolamine, diethanolamine and triethanoloamine. Water-solubleorganic solvents useful as developers include isopropyl alcohol, benzylalcohol, ethyl cellosolve, butyl cellosolve, diacetone alcohol and thelike. Depending on particular needs, the developing solution may containsurfactants, dyes, salts for inhibiting the swelling of the photoresist,or salts for corroding the metal substrate.

As another means of development, it is noted that the present inventionis especially well suited for several on-press development systems. Forexample, good results have been accomplished using the photoreactivepolymeric binders of the present invention in a photoresist that is incontact or brought into contact with the microencapsulated developersystems described in U.S. patent application Ser. No. 08/146,710,cross-referenced above. The photoresist also incorporated a plasticizingsystem and a dispersed, particulate rubber system, as described in theabove cross-referenced U.S. patent applications Ser. Nos. 08/147,044 and08/146,479, respectively. See, Example 6, infra, for a representativeexample.

The present invention will now be described in further detail by thefollowing non-limiting examples of several of its embodiments. Unlessotherwise indicated, all parts, percents, ratios and the like are byweight.

EXAMPLES Preparation of Photopolymer 1

In a 500 ml, three-necked, round bottom flask fitted with a 250 mladdition funnel with a dry N₂ inlet, a Claisen adapter bearing a septum,and a condenser with an exit to a gas bubbler, toluene (30 g) wassparged for 5 minutes with N₂. In the addition funnel, a solution ofm-isopropenyl-α,α-dimethyl isocyanate (13.5 g), methyl methacrylate(41.0 g), butyl methacrylate (45.5 g), toluene (50 g), and t-butylperoxybenzoate (0.2 g) was sparged for 15 minutes with N₂.

The stirred toluene was brought to reflux in a 120° C. bath and thecontents of the addition funnel were added over 2 hours. After refluxingan additional 6 hours, a 5% solution of BHT in toluene (10 g) was added.Dry air was then introduced and heating discontinued. After 15 minutes,4-hydroxybutyl acrylate (11.62 g), triethylamine (2 g of a 10% solution)and dibutyl tin dilaurate (2 g of a 10% solution) were added and thesolution is heated at 80° C. for 21 hours. Methanol (10 g) wassubsequently added and after heating for 0.5 hrs, 187.4 g of reactionsolution was poured into a brown polyethylene bottle.

A 100 g portion of the reaction solution, diluted with methyl ethylketone (50 g) was mixed into stirred hexanes (3 L) giving a soft amberprecipitate (˜75 g). The amber precipitate was dissolved in acetone (150g) and reprecipitated over 2 hours in stirred methanol (3 L). A stringy,white precipitant was collected by vacuum filtration, rinsed withmethanol (2×100 ml), broken into small pieces and air dried overnight.31.1 g of white precipitant was retrieved (31.1 g, 53% yield). GPC: Mw116,221: Mn 58,875; DSC: Tg 72° C.

Preparation of Photopolymer 2

By the procedure described for the preparation of Photopolymer 1,m-isopropenyl-α,α-dimethyl isocyanate (13.5 g), methyl methacrylate (63g), butyl methacrylate (23.5 g), toluene (50 g) and t-butylperoxybenzoate (0.2 g) were used in polymerization, followed by thederivatization with 4-hydroxybutyl acrylate (11.6 g) to give 27.4 g ofsolid (47.0%). GPC: Mw 113,099; Mn 55,775; DSC: Tg 90° C.

Preparation of Photopolymer 3

Photopolymer 3 was prepared in the same manner as Photopolymer 2, except1 g of maleic anhydride was used to replace 1 g of the methylmethacrylate in the monomer feed, giving 36.55 g of solid (74.4%). GPC:Mw 140,765; Mn 52,768; DSC: Tg 87° C.

Preparation of Photopolymer 4

Photopolymer 4 was prepared in the same manner as Photopolymer 2, except15 g of m-isopropenyl-α,α-dimethyl isocyanate, 61.5 g of methylmethacrylate, 23.5 g of butyl methacrylate and 1.25 g of t-butylperoxybenzoate were used in the monomer feed, giving a 65.5% yield. GPC:Mw 33750; Mn 11400; DSC: Tg 72° C.

Preparation of Photopolymer 5

Photopolymer 5 was prepared in the same manner as Photopolymer 4, except1.25 g of methyl methacrylate were substituted with 1.25 g of maleicanhydride, giving a 77% yield. GPC: Mw 54625, Mn 15636; DSC: Tg 82° C.

Preparation of Photopolymer 6

By the procedure described for Photopolymer 1,m-isopropenyl-α,α-dimethyl isocyanate (13.5 g), methyl methacrylate (62g), butyl methacrylate (23.5 g), toluene (50 g) and t-butylperoxybenzoate (0.5 g) were used in the polymerization. In thesubsequent derivatization, 4-hydroxybutyl acrylate (8.7 g),triethylamine (2 g of a 10% soln.) and dibutyl tin dilaurate (10 g of a10% soln.) were utilized and the solution heated at 80° C. for 21 hours.Methanol (20 g) was added. After heating 0.5 hours, an amber solutionwas obtained (198.73 g, 43.4% solids, 78% yield). GPC: Mw 86,000; Mn37,000; DSC: Tg 76.7° C. This solution was used directly in formulatinga photoresist layer.

Preparation of Photopolymer 7

Preparation of Photopolymer 7 was the same as Photopolymer 6, except 1 gof maleic anhydride replaced 1 g of the methyl methacrylate in themonomer feed, giving an amber solution (191.73 g, 49.93% solids, 87%yield). GPC: Mw 145,000; Mn 36,000; DSC: Tg 88.4° C. This solution wasused directly in formulating a photoresist layer.

The efficacy of the maleic anhydride acceleration mechanism used in thepreparation of Photopolymers 3, 5, and 7 will be evident from theresults summarized in Table 1, below.

                                      TABLE 1    __________________________________________________________________________    Maleic Anhydride as the    "Match Maker" For TMI/Acrylate Copolymerization                 Photo-      Photo-      Photo-           Photo-                 polymer 3                       Photo-                             polymer 5                                   Photo-                                         polymer 7           polymer 2                 w/MA  polymer 4                             w/MA  polymer 6                                         w/MA    __________________________________________________________________________    Wt % m-TMI           13.5  13.5  15    15    13.5  13.5    Wt % MMA           63    62    61.5  60.25 63.0  62    Wt % BMA           23.5  23.5  23.5  23.5  23.5  23.5    Wt % MA           0     1     0     1.25  0.0   1.0    % Initiator           0.2   0.2   1.25  1.25  0.5   0.5    Mw     113099                 140765                       33750 54625 86000 145000    Mn     55775 52768 11400 15636 37000 36000    % Yield           47    74    65.5  77    78    87    __________________________________________________________________________

As shown in Table 1, the use of 1% maleic anhydride in the synthesis ofPhotopolymers 3 and 7 gave lower residual monomer and higher weightaverage molecular weight than the corresponding Photopolymers 2 and 6.Likewise the use of 1.25% maleic anhydride in the synthesis ofPhotopolymer 5 shows a higher conversion and molecular weight than thecorresponding Photopolymer 4 synthesized without maleic anhydride.

Preparation of Photopolymer 8

In a 2 L, three-necked, round bottom flask fitted with a mechanicalstirrer; dry N₂ inlet; fluid metering pump delivery tube; and Claisenadapter bearing a thermometer and a condenser with an exit to a gasbubbler, toluene (140 g) was sparged for 5 minutes with N₂. In anaddition pump reservoir, a solution of m-isopropenyl-α,α-dimethylisocyanate (44.3 g), maleic anhydride (8.87 g), methyl methacrylate(285.9 g), butyl methacrylate (104.16 g), toluene (191.69 g) and t-butylperoxybenzoate (1.55 g) was sparged for 15 minutes with N₂.

The initial charge was stirred (150 rpm) and brought to reflux in a 120°C. bath, whereupon a solution of t-butyl peroxybenzoate (0.66 g) intoluene (10 g) was injected, and the contents of the feed reservoir weremetered out for a period of 6 hours. After heating an additional 2hours, a 10% solution of ethyl 4-N,N-dimethylaminobenzoate (EPD) intoluene (23.05 g) was added under dry N₂ and heating discontinued. After30 minutes, 4-hydroxybutyl acrylate (40.01 g), BHT (44.33 g of a 5%solution), DBTDL (44.33 g of a 10% solution) and dry air wereintroduced, and the solution heated at 80° C. for 16 hours. Methanol (50g) was added, and after heating for 0.5 hours, 957.3 g of a reactionsolution was obtained (40.2% solids, theory: 50%), giving a 78% yield.GPC: Mw 107,000; Mn 35,000; DSC: Tg 90.4° C. This solution was useddirectly in formulating a photoresist layer.

Preparation of Photopolymer 9

By the procedure described for the preparation of Photopolymer 8,m-isopropenyl-α,α-dimethylbenzyl isocyanate (44.3 g), maleic anhydride(11.08 g), methyl methacrylate (283.68 g), butyl methacrylate (104.16g), toluene (346.72 g) and t-butyl peroxybenzoate (4.42 g) were used inthe polymerization, followed by derivatization with 4-hydroxybutylacrylate (30.16 g). 935.8 g of solution was obtained (51.82% solids;theory 986.03 g, 49.4%), constituting a 99.6% yield. GPC: Mw 127,029; Mn22,500; DSC: Tg 75° C.

Preparation of Photopolymer Rx-2

In the manner of the procedures described for the preparation ofPhotopolymers 1 to 9, Photopolymer Rx-2 is prepared in accordance withthe following tabulated protocol.

    ______________________________________    STEPS:    Components          % wt    wt (g)  mole %    ______________________________________    INITIAL CHARGE:    Maleic Anhydride    8.5     0.75    0.11    m-TMI               17.5    1.552   0.10    Methyl Methacrylate 56      4.96    0.65    Butyl Methacrylate  18      1.596   0.15    Toluene             --      32      --    ADDITION I    (Under Dry Nitrogen):    t-Butyl Peroxybenzoate                        --      0.396   --    Toluene             --      2       --    ADDITION II    (Under Dry Nitrogen):    Maleic Anhydride    8.5     6.78    0.10    m-TMI               17.5    13.962  0.10    Methyl Methacrylate 56      44.67   0.65    Butyl Methacrylate  18      14.361  0.15    Toluene             --      35.344  --    t-butyl Peroxybenzoate                        --      0.93    --    QUENCH I    (Under Dry Nitrogen):    Ethyl 4-N,N-Dimethylaminobenzoate,                        --      4.61    --    10%    DERIVATIZATION    (Under Dry Air):    4-Hydroxybutyl Acrylate                        --      10.56   0.10    Dibutyl Tin Dilaurate, 10%                        --      8.866   --    2,6-Di-t-Butyl-4-methylphenol, 5%                        --      8.866   --    QUENCH II:    Methanol            --      10      --    ______________________________________

202.203 g of solution was obtained (50.60% solids). GPC: Mw 100,300; Mn17,959; DSC: Tg 88.7° C. (onset), 96.6° C. (midpoint); m-TMI-HBA PendantVinyl: 9.5 mole %.

EXAMPLE 1

An aluminum substrate was electrochemically grained and anodized to givea porous aluminum oxide surface. This surface was then treated with apolymeric acid to produce an aluminum plate which was suitable forlithographic printing. A solution was then prepared based on theformulation in Table 2.

                  TABLE 2    ______________________________________    Component                   % Solids    ______________________________________    Photopolymer 1              56.35    Hexafunctional Urethane Acrylate                                10.70    (Ebecryl 8301 from Radcure)    Difunctional Urethane Acrylate (PU788 from Morton)                                2.88    Trimethylolpropane triacrylate                                4.76    Cab-o-Sil M5 Silica         1.00    Hycar Rubber (1300 × 33 from B.F. Goodrich)                                4.00    3-benzoyl-7-methoxycoumarin 1.40    [4-(4-methylphenylthio)phenyl]-phenylmethanone                                1.80    2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2-                                3.50    biimidazole    Diphenyl Phosphate          2.25    4,4'-methylenebis-(2,6-diisopropyl-N,N-dimethylaniline)                                2.25    Pluronic L43 (from BASF)    2.50    Triethylene Glycol Diacetate                                3.00    Lithium Chloride            0.62    Leuco Crystal Violet        3.00    2,6-di-(t-butyl)-4-methylphenol                                0.14    Ciba-Geigy Irganox 1035     0.10    ______________________________________

A 7% solution of the formulation in MEK/Toluene was spin coated onto aplate at a spin rate of 200 rpm.

The coated plate was then exposed to actinic radiation from a standardmercury halide lamp, which had an emission peak in the ultraviolet rangeat 364 nm. The plate was then exposed through an UGRA target mask toproduce a test image. The plate was then developed with a mixture of 55%ethyl acetate and 45% isopropanol, washed with 60% ethyl acetate and 40%isopropanol, and dried in a 70° C. oven for 10 minutes. The developedplate was subsequently gummed with a protective finisher, and storedunder ambient conditions.

The plate was then placed on a Komori printing press and run in standardoperation. The plate was run continuously for more than 50,000 goodimpressions.

EXAMPLE 2 (COMPARATIVE)

A formulation identical to that in table 2 was coated on an aluminumsubstrate in the same manner as in Example 1, except that 19.6%poly(methyl methacrylate), i.e. Acryloid Resin A-11 from Rohm & Haas,and 36.75% of a 50/50 copolymer of ethyl methacrylate and methylacrylate, i.e. Acryloid Resin B-72 from Rohm & Haas, were substitutedfor Photopolymer 1. When this plate was exposed and developed underconditions identical to those of the previous example, the photoresistdegraded to a state of practical uselessness before the completion of1000 impressions.

EXAMPLE 3

Photopolymer 2 (0% maleic anhydride) and Photopolymer 3 (1% maleicanhydride) were tested using the same aluminum substrate and formulationset forth in Example 1, except for a lower binder to monomer ratio.Their compositions are shown in Table 3.

                                      TABLE 3    __________________________________________________________________________    Component                    Plate 3A                                      Plate 3B    __________________________________________________________________________    Photopolymer 2 (0% maleic anhydride)                                 40.25                                      --    Photopolymer 3 (1% maleic anhydride)                                 --   40.25    Hexafunctional Urethane Acrylate                                 18.1 18.1    (Ebecryl 8301 from Radcure)    Difunctional Urethane Acrylate (PU788 from Morton)                                 5.40 5.40    Trimethylolpropane triacrylate                                 8.93 8.93    Cab-o-Sil M5 Silica          1.00 1.00    Hycar Rubber (1300 × 33 from B.F. Goodrich)                                 4.00 4.00    3-benzoyl-7-methoxycoumarin  1.40 1.40    [4-(4-methylphenylthio)phenyl]-phenylmethanone                                 1.80 1.80    2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2-biimidazole                                 3.50 3.50    Diphenyl Phosphate           2.25 2.25    4,4'-methylenebis-(2,6-diisopropyl-N,N-dimethylaniline)                                 2.25 2.25    Pluronic LA3 (from BASF)     2.50 2.50    Triethylene Glycol Diacetate 3.00 3.00    Lithium Chloride             0.62 0.62    Leuco Crystal Violet         3.00 3.00    2,6-di-(t-butyl)-4-methylphenol                                 0.14 0.14    Irganox 1035 (from Ciba-Geigy)                                 0.10 0.10    __________________________________________________________________________

Both plates were exposed through an UGRA target mask and a step wedge (3step/stop), developed by solvents and gummed as described in Example 1.Both plates could be run for more than 50,000 good impressions. However,Photopolymer 3 (1% maleic anhydride) showed roughly a 25% fasterphotospeed than Photopolymer 2 (0% maleic anhydride).

EXAMPLE 4

Photopolymers 6 (0% maleic anhydride) and Photopolymer 7 (1% maleicanhydride) were tested using the same aluminum substrate and formulationset forth in Example 1, except for a lower binder to monomer ratio.Their compositions are shown in Table 4:

                                      TABLE 4    __________________________________________________________________________    Component                    Plate 4A                                      Plate 4B    __________________________________________________________________________    Photopolymer 6 (0% maleic anhydride)                                 49.00                                      --    Photopolymer 7 (1% maleic anhydride)                                 --   49.00    Hexafunctional Urethane Acrylate                                 15.57                                      15.57    (Ebecryl 8301 from Radcure)    Difunctional Urethane Acrylate (PU788 from Morton)                                 4.19 4.19    Trimethylolpropane triacrylate                                 6.92 6.92    Cab-o-Sil M5 Silica          1.00 1.00    Hycar Rubber (1300 × 33 from B.F. Goodrich)                                 4.00 4.00    3-benzoyl-7-methoxycoumarin  1.40 1.40    [4-(4-methylphenylthio)phenyl]-phenylmethanone                                 1.80 1.80    2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2-biimidazole                                 3.50 3.50    Diphenyl Phosphate           2.25 2.25    4,4'-methylenebis-(2,6-diisopropyl-N,N-dimethylaniline)                                 2.25 2.25    Pluronic L43 (from BASF)     2.50 2.50    Triethylene Glycol Diacetate 3.00 3.00    Lithium Chloride             0.62 0.62    Leuco Crystal Violet         3.00 3.00    2,6-di-(t-butyl)-4-methylphenol                                 0.14 0.14    Ciba-Geigy Irganox 1035      0.10 0.10    __________________________________________________________________________

After exposure at 2.5, 5, 7.5, 10 and 40 LU, solvent development, andgumming as in Example 1, the plates were run on a Multigraphics FormPress for 50,000 impressions. Plate 4B (Photopolymer 7) showed aninitial maximum step Dmax of 3 (7.5 LU), dropping back to 2 andremaining steady for the run. At 5 LU, 2% highlight dot decreased to 3%by 15,000 impressions, where it remained through the run. In contrast,Plate 4A (Photopolymer 6) required 10 LU for an initial step Dmax of 3which dropped to 1 by 25,000 impressions. At 7.5 LU, the step Dmax was 2and dropped to 1 and highlight dot was 3% dropped to 5% by 50,000impressions. Again, the performance of the photopolymer containing 1%maleic anhydride was superior to the photopolymer containing no maleicanhydride.

EXAMPLE 5

Photopolymer 8 (2% maleic anhydride) was tested using the same aluminumsubstrate and formulation set forth in Example 1, except for a lowerbinder to monomer ratio. The composition is shown in Table 5:

                  TABLE 5    ______________________________________    Component                   % Solids    ______________________________________    Photopolymer 8 (2% maleic anhydride)                                49.00    Hexafunctional Urethane Acrylate                                15.57    (Ebecryl 8301 from Radcure)    Difunctional Urethane Acrylate (PU788 from Morton)                                4.19    Trimethylolpropane triacrylate                                6.92    Cab-o-Sil M5 Silica         1.00    Hycar Rubber (1300 × 33 from B.F. Goodrich)                                4.00    3-benzoyl-7-methoxycoumarin 1.40    [4-(4-methylphenylthio)phenyl]-phenylmethanone                                1.80    2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2-                                3.50    biimidazole    Diphenyl Phosphate          2.25    4,4'-methylenebis-(2,6-diisopropyl-N,N-dimethylaniline)                                2.25    Pluronic L43 (from BASF)    2.50    Triethylene Glycol Diacetate                                3.00    Lithium Chloride            0.62    Leuco Crystal Violet        3.00    2,6-di-(t-butyl)-4-methylphenol                                0.14    Irganox 1035 (from Ciba-Geigy)                                0.10    ______________________________________

After exposure at 2.5, 5, 7.5, 10 and 20 LU, solvent development andgumming as in Example 1, the plate was run on a Komori printing pressfor 100,000 impressions. At 10 LU, initial 2% highlight dot coverage onpaper remained above 100,000 impressions. At 7.5 LU, 2% highlight dotdropped to 3% by 60,000 impressions, where it remained through the run.

EXAMPLE 6

A photoresist solution with 7% of solid was made according to theformulation set forth below. The photoresist solution contained aphotoreactive polymeric binder prepared in accordance with the presentinvention:

    ______________________________________    Component                  % (w/w)    ______________________________________    Photoreactive Acrylic Binder*                               51.75    Ebecryl 8301 oligomer (from Radcure)                               17.42    Trimethylolpropane triacrylate                               4.68    Polyurethane PU788 (from Morton)                               7.74    Acrylated Nitrile Butadiene (Hycar 1300 × 33,                               4.00    Goodrich)    3-benzoyl-7-methoxy coumarin**                               1.40    4-benzoyl-4-methyl diphenyl sulfide**                               1.80    2-phenyl-4,6-bis-(trichloromethyl-5-triazine)**                               2.21    Triethylene glycol diacetate                               3.50    Leuco Crystal Violet Dye   2.77    2,6-di-tert-butyl-4-methyl phenol (BHT)***                               0.13    Irganox 1035 (from Ciba-Geigy)                               0.10    Pluronic L43 Surfactant (from BASF)                               2.50    ______________________________________     Notes:     *The photoreactive binder contained methyl methacrylate, butyl     methacrylate, maleic anhydride, and an mTMI adduct with hydroxybutyl     acrylate;     **Radical initiator;     ***Antioxidant.

The photoresist composition was coated onto an anodized aluminum plateby continuous roll coating, exposed to actinic radiation, then on-pressdeveloped. On-press development of the photoresist was effectuated bythe agency of high-boiling, low-vapor pressure developers liberated fromruptured microcapsules coated atop the photoresist.

The microcapsules were prepared by first dissolving 8.0 g HEC 330 PA(from Hercules), 3.9 g Versa TL 502 (from National Starch), 0.06 gAerosol OT (from Fisher) in 425 g H₂ O. A mixture of 21.5 g gammanonalactone, 89.5 g dibutyl phthalate, and 11.1 g Desmodur N-100 (fromMiles) was then dispersed into the aqueous phase at 1500 rpm for 10minutes. To encourage the formation of prewall, a small amount ofdibutyl tin dilaurate (0.12 g) was added into the oleophilic phase. 1.4g of triethylene tetramine was added and allowed to react for 2 hours atroom temperature. 41.1 g of a melamine-formaldehyde prepolymer (CYMEL385, from American Cyanamid) was added and the pH adjusted to between 5and 5.5 with 1N sulfuric acid. The reaction was continued at 65° C. forone hour. 10.0 gs of urea were added to react for one hour to quench allresidual formaldehyde and/or melamine-formaldehyde condensate in themixture. Sodium Chloride (18.3 g) was added and the pH was brought to 9and the reaction allowed to continue for 30 minutes, then slowly cooledto 25° C. The microcapsules were washed extensively with deionized waterin a centrifuge.

A microcapsule-containing coating solution was subsequently preparedutilizing 9.45 g microcapsules (at 39.7% w/v), 0.47 g Silica 2040 (at40% w/v), 1.13 g PVA 205 (at 10% w/v), 2.24 g Pluronic L43 surfactant(at 5% w/v); Tx100 surfactant (at 10% w/v), 0.06 g LiCl (at 2% w/v) and11.47 g H₂ O.

The microcapsule-containing coating solution was coated atop thephotoresist. After exposing the plate to 40 UV light units, the platewas run through a pressure roller then mounted and ran on aMultigraphics 1250 lithographic printing press. The plate on-pressdeveloped within 20 impressions.

We claim:
 1. A photoreactive polymeric binder of the formula: ##STR5##wherein n is an integer from 1 to 18; --M-- is one or more polymerizedunits of ethylenically unsaturated monomers;y is approximately 70% toapproximately 95% by weight, z is from approximately 5% to approximately30% by weight, and the sum of v and x are from greater than 0% toapproximately 10% by weight; R₁ is H, or alkyl; and R₂ and R₃ are eachH, alkyl, aryl, or --(CH₂)_(n) O₂ CCH═CH₂.
 2. The photoreactivepolymeric binder of claim 1, wherein n is an integer from 2 to
 6. 3. Thephotoreactive polymeric binder of claim 1 wherein either R₂ or R₃ is--(CH₂)_(n) O₂ CCH═CH₂.
 4. A method for synthesizing photoreactivepolymeric binders comprising the steps ofcopolymerizing anm-isopropenyl-α,α-dimethylbenzyl isocyanate monomer with an electrondeficient comonomer and a substituted comonomer of the formula CH₂ ═CR₁R₂, wherein R₁ and R₂ are each H, Cl, alkyl, --CO₂ CH₃, --CO₂ CH₂ CH₃,--CO₂ Bu, --CO₂ C₈ H₁₇, --CO₂ C₁₂ H₂₅, --CO₂ Ph, --CO₂ CH₂ CH₂ N(CH₃)₂,--Ph, --CN, --C₆ H₄ CH₂ C₁, --C₆ H₄ N, --F, --COOH, --SO₃ H, or theirsalts; and derivatizing the copolymer with a hydroxyalkyl acrylate ofthe formula HO(CH₂)_(n) O₂ CCH═CH₂, wherein n is an integer from 1 to18.
 5. The method of claim 4, wherein the concentration of them-isopropenyl-α,α-dimethylbenzyl isocyanate monomer is fromapproximately 5% to approximately 30% by weight, the concentration ofthe electron deficient monomer is from greater than 0% to approximately10% by weight, and the total concentration of the substituted comonomersis from approximately 70% to approximately 95% by weight.
 6. The methodof claim 4, wherein the electron deficient comonomer is a maleicanhydride comonomer.